Diversity-Oriented Synthesis of a Library of Star-Shaped 2<i>H</i>‑Imidazolines

A library of star-shaped 2<i>H</i>-imidazolines has been synthesized via Debus–Radziszewski condensation from 1,2-diketones and ketone starting materials. Selective reduction of one imine group of the 2<i>H</i>-imidazole intermediate with LiAlH₄ or catalytic flow hydrogenation furnished 2<i>H</i>-imidazolines, which could be conveniently diversified by reacting the amine <i>N</i> with electrophiles, resulting in a set of 21 amide-, carbamate-, urea-, and allylamine-containing products. In total, five points of diversification could be used, which allow the production of a set of functionally diverse compounds. The synthesis of acylated 2<i>H</i>-imidazolidines resulted in intrinsically labile compounds, which spontaneously degraded to acyclic derivatives, as shown for the reaction of 2<i>H</i>-imidazolidine with hexylisocyanate